arXiv subjects
Publications and source records attributed to A. K. Mohapatra.
The formation of rf-dressed Rydberg dark states in thermal Rb vapour is demonstrated. It is shown that such states exhibit enhanced sensitivity to dc electric fields compared to their bare counterparts and enable precise measurement of the dc field independent of laser frequency fluctuations.
We demonstrate laser frequency stabilization to excited state transitions using cascade electromagnetically induced transparency (EIT). Using a room temperature Rb vapor cell as a reference, we stabilize a first diode laser to the D2 transition and a second laser to a transition from the intermediate state to a Rydberg state with principal quantum number n=19 - 70. A combined laser linewidth of 280 kHz over a 0.1 ms time period is achieved. This method may be applied generally to any cascade system and allows laser stabilization to an atomic reference in the absence of strong optical transitions.
We study the effect of a control beam on a Lambda electromagnetically induced transparency (EIT) system in 87Rb. The control beam couples one ground state to another excited state forming a four level N-system. Phase coherent beams to drive the N-system are produced using a double injection scheme. We show that the control beam can be used to Stark shift or split the EIT resonance. Finally, we show that the when the control beam is on-resonance one observes a Doppler-free and sub-natural absorptive resonance with a width of order 100 kHz. Crucially, this narrow absorptive resonance only occurs when atoms with a range of velocities are present, as is the case in a room temperature vapour.
The electro-optic effect, where the refractive index of a medium is modified by an electric field, is of central importance in non-linear optics, laser technology, quantum optics and optical communications. In general, electro-optic coefficients are very weak and a medium with a giant electro-optic coefficient would have profound implications for non-linear optics, especially at the single photon level, enabling single photon entanglement and switching. Here we propose and demonstrate a giant electro-optic effect based on polarizable dark states. We demonstrate phase modulation of the light field in the dark state medium and measure an electro-optic coefficient that is more than 12 orders of magnitude larger than in other gases. This enormous Kerr non-linearity also creates the potential for precision electrometry and photon entanglement.
We study electromagnetically induced transparency (EIT) of a weakly interacting cold Rydberg gas. We show that the onset of interactions is manifest as a depopulation of the Rydberg state and numerically model this effect by adding a density-dependent non-linear term to the optical Bloch equations. In the limit of a weak probe where the depopulation effect is negligible, we observe no evidence of interaction induced decoherence and obtain a narrow Rydberg dark resonance with a linewidth of <600 kHz, limited by the Rabi frequency of the coupling beam
We demonstrate a multiphoton Rydberg dark resonance where a Lambda-system is coupled to a Rydberg state. This N-type level scheme combines the ability to slow and store light pulses associated with long lived ground state superpositions, with the strongly interacting character of Rydberg states. For the nd_{5/2} Rydberg state in 87Rb (with n=26 or 44) and a beam size of 1 mm we observe a resonance linewidth of less than 100 kHz in a room temperature atomic ensemble limited by transit-time broadening. The resonance is switchable with an electric field of order 1 V/cm. We show that, even when photons with different wavevectors are involved, the resonance can be Doppler-free. Applications in electro-optic switching and photonic phase gates are discussed.
We observe electromagnetically induced transparency (EIT) on the 5s to 5p transition in a room temperature rubidium vapour cell by coupling the 5p state to a Rydberg state (ns or nd with n=26 to 124). We demonstrate that the narrow line-width of the EIT resonance (2 MHz) allows precise measurement of the d state fine structure splitting, and together with the sensitivity of the Rydberg state to electric fields, we are able to detect transient electric fields produced by the dynamics of charges within the cell. Coherent coupling of Rydberg states via EIT could also be used for cross-phase modulation and photon entanglement.
We have constructed a high-$p_T$ trigger for the HERA-B experiment at DESY. The HERA-B experiment produces B mesons by inserting wire targets into the halo of the proton beam circulating in HERA. The high-\pt trigger records events that contain tracks that have high transverse momentum with respect to the beam. Such a trigger is efficient for recording $B \to π^+π^-$, $B \to K^-π^+$, $B_s \to K^+ K^-$, $B_s \to D_s^-π^+$, and other topical hadronic B decays. These decays provide sensitivity to the internal angles $α$ and $γ$ of the CKM unitarity triangle, and they also can be used to measure or constrain the $B_s$-$\bar B_s$ mixing parameter $x_s$.